Topic 27 classes and objects state and behavior PDF

Classes and objects in Java

Note that code examples in this tutorial compile and run under Java 12. Advanced techniques: Fields and methods in Java. TABLE OF CONTENTS. • Class declaration.

Chapter 8: Objects and Classes

❑ The Java API has many classes that provide methods you can use without instantiating objects. ▫ The Math class is an example we have used. ▫ Math.sqrt

Classes and Objects in Java

object and enables one object to interact with other objects. Example of an object : dog. Objects correspond to things found in the real world. For example ...

Objects and Classes in Java

Let's see a simple example where we are going to initialize the object through a reference variable. File: TestStudent2.java class Student{ int id;. String name

Java Code Conventions

4 Oct 1996 class Sample extends Object { int ivar1; int ivar2;. Sample(int i ... The following example shows how to format a Java source file containing a ...

Objects in Java Classes in Java

Example: A dog has states - color name

Writing New Java Classes

• A Java class definition contains The fields (instance variables) of an object are the variables that define an object's properties. Example: An object from ...

Untitled

The following is example syntax to create a programmer- created object class. • The Java keywords are: – package (optional). – import (optional). – public

Java Questions for Practice and Assignment Short Answer Type: 1

Write difference between class and object? 14. What is constructor. Give example? 15. Write the use of static and this keywords using example? 16.

Objects and Classes in Java

Let's see a simple example where we are going to initialize the object through a reference variable. File: TestStudent2.java class Student{ int id;. String name

Java - Object & Classes

A class can have any number of methods to access the value of various kinds of methods. In the above example barking

Topic 27 classes and objects state and behavior

objects. – Example: Zombies is a client of DrawingPanel and Graphics. Zombie.java (client program) public class Zombie { main(String[] args) {.

Objects and JUnit

reference types (implemented as Java classes). Each new release of Java tends to add new reference types. For example instances of the Java String class

Java Code Conventions

4 oct. 1996 For an example of a Java program properly formatted see “Java ... Avoid using an object to access a class (static) variable or method.

Classes and Objects

Classes and Objects Object. Holds a data type value; variable name refers to object. In Java ... Sample from an N-by-N grid of points in the plane.

Object-oriented programming with Java Classes and objects

For example we can have an Executive class that derives from Manager. Employee. Manager. Secretary. Programmer. Executive. 52. Inheritance hierarchies.

Hardware Objects for Java

represent I/O devices as first class Java objects where device an example of the control flow for a web server application.

OBJECT-ORIENTED DESIGN AND IMPLEMENTATION

Use of so-called “Object-Oriented language” such as C++ or Java does not guarantee Figure 1 is an example class diagram taken from Geant4 toolkit[1].

IBM Security Access Manager for Web Version 7.0: Administration

The Javadoc information associated with the administration Java classes methods

Java Basic Refresher - Stanford University

Student Java Example • As a first example of a java class we'll look at a simple "Student" class Each Student object stores an integer number of units and responds to messages like getUnits() and getStress() The stress of a student is defined to be units * 10 Implementation vs Interface Style • In OOP every class has two sides • 1

Object-Oriented Programming with Java Tutorial

Classes and objects A class is a template from which objects may be created Can have any number of instances (objects) An object contains state (data) and behavior (methods) Methods of an object collectively characterize its behavior Methods can only be invoked by sending messages to an object Behavior is shared among objects 2

Java Class Vs Object – How To Use Class And Object In Java

• Every object has a class – A class defines methods and fields – Methods and fields collectively known as members • Class defines both type and implementation – type ? where the object can be used – implementation ? how the object does things • Loosely speaking the methods of a class are its Application Programming Interface

32 Classes Objects Methods and Instance Variables

(C orm Methods 2 and ont ) ore attributes variables Carried with theobjectasit is used 3 3Declaring Instantiating Eachclass C anlassw Object declarationthat itha ofa 3 and Method lass begins publicmustbe nameastheclass nameextension storedin andends file with withkeyword thathasthesame the javafile- lass k o o B e d a r G 4 keyw C lass ordpublic

The Java Object Model - University of San Francisco

When a class referencesanother class the Java compiler finds the associated class definition to performtype checking and so on For example Employee references String which thecompiler finds in file String class stored in the standard Java class library Variable Definitions Variable definitions are of the form: modifiers TypeName name;

Searches related to example for class and object in java filetype:pdf

class: A program entity that represents either: 1 A program / module or 2 A template for a new type of objects –The DrawingPanelclass is a template for creating DrawingPanelobjects –Other classes: String Random Scanner File object: An entity that combines state and behavior

[PDF] Objects and Classes in Java

In this page we will learn about Java objects and classes In object-oriented The example of an intangible object is the banking system

[PDF] Java - Object & Classes - Tutorialspoint

Class - A class can be defined as a template/blue print that describes the behaviors/states that object of its type support Objects in Java:

[PDF] Chapter 8: Objects and Classes

Java programs are made of objects that interact A class describes a set of objects with the same For example the String class provides methods:

[PDF] Classes and objects in Java

Learn how to make classes fields methods constructors and objects work This tutorial teaches you how to declare classes describe attributes via

[PDF] Objects in Java Classes in Java

Example: A dog has states - color name breed as well as behaviors – wagging the tail barking eating An object is an instance of a class Objects in Java

[PDF] Object-oriented programming with Java Classes and objects

Classes and objects • A class is a template from which objects may be created – Can have any number of instances (objects) • An object contains state

[PDF] Classes and Objects - MIT OpenCourseWare

Today's Topics Object oriented programming Defining Classes Using Classes References vs Values Static types and methods

[PDF] Objects and Classes

Introduce you to object-oriented programming • Show you how you can create objects that belong to classes in the standard Java library

Java Class and Objects (With Example) - Programiz

In this tutorial you will learn about the concept of classes and objects in Java with the help of examples Java is an object-oriented programming language

[PDF] Java - Object & Classes

Class - A class can be defined as a template/blue print that describes the behaviors/states that object of its type support Objects in Java:

What is the difference between a class and an object in Java?

While a class in Java is only a logical unit, an object in Java is both a physical and logical entity. What is an object in Java? An object is an entity that has a state and exhibit behavior. For example, any real-life entity like a pen, a laptop, a mobile, a table, a chair, a car, etc. is an object.

What is the purpose of classes and objects in Java?

Classes and Objects in Java, or any other Object-Oriented Programming Language, form the basis of the language. Classes allow a user to create complex data structures by logically grouping simple data structures.

What data is associated with a class or object in Java?

Everything in Java is associated with classes and objects, along with its attributes and methods. For example: in real life, a car is an object. The car has attributes, such as weight and color, and methods, such as drive and brake. A Class is like an object constructor, or a "blueprint" for creating objects.

How do I use classes to create objects in Java?

In Java, an object is created from a class. We have already created the class named Main, so now we can use this to create objects. To create an object of Main, specify the class name, followed by the object name, and use the keyword new: You can also create an object of a class and access it in another class.

Topic 27

classes and objects, state and behavior

Copyright Pearson Education, 2010

Based on slides by Marty Stepp and Stuart Reges

from http://www.buildingjavaprograms.com/ "A 'class' is where we teach an 'object' to behave." -Rich Pattis 2

Object Oriented Programming

"Object-oriented programming is a method of programming based on a hierarchy of classes, and well-defined and cooperating objects. "

What is a class?

"A class is a structure that defines the data and the methods to work on that data. When you write programs in the Java language, all program data is wrapped in a class, whether it is a class you write or a class you use from the Java platform API libraries." a new data type

Object Oriented Programming

In other words break the problem up based

on the things / data types that are part of the problem

Not the only way

One of many different kinds of strategies or

paradigms for software development functional, procedural, event driven, data flow, formal methods, agile or extreme, ... 3

Clicker 1

What kind of assignment handout

do you prefer?

A.A long assignment handout

B.A short assignment handout

Why? 4 5

Example -Monopoly

If we had to start

from scratch what classes would we need to create?

Classes Needed:

A programming problem

Given a file of cities' (x, y) coordinates,

which begins with the number of cities: 6 50 20
90 60
10 72 74 98
5 136

150 91

Write a program to draw the cities on a

DrawingPanel, then a terrible event occurs

(zombie apocalypse, nuclear meltdown) that turns all cities red that are within a given radius:

Ground zero x: 100

Ground zero y: 100

Area of effect: 75

A solution

Scanner input

= new Scanner(new File("cities.txt")); int cityCount = input.nextInt(); int[] xCoords = new int[cityCount]; int[] yCoords = new int[cityCount]; for (int i = 0; i < cityCount; i++) { xCoords[i] = input.nextInt(); yCoords[i] = input.nextInt(); parallel arrays: 2+ arrays with related data at same indexes. Considered poor style. (Relationship exists in the 7

Observations

The data in this problem is a set of points.

An alternative is to store them as Point

objects.

A Pointwould store a city's x/y data.

We could compare distances between Points

to see whether the terrible event affects a given city.

Each Pointwould know how to draw itself.

The driver program would be shorter

and cleaner. 8

Clients of objects

client program: A program that uses objects.

Example: Zombiesis a client of DrawingPanel

and Graphics.

Zombie.java(client program)

public class Zombie { main(String[] args) { new DrawingPanel(...) new DrawingPanel(...)

DrawingPanel.java(class)

public class DrawingPanel { 9

Classes and objects

class: A program entity that represents either:

1.A program / module, or

2.A template for a new type of objects.

The DrawingPanelclass is a template for

creating DrawingPanelobjects. object: An entity that combines state and behavior. object-oriented programming (OOP): Programs that perform their behavior as interactions between objects. 10

Blueprint analogy

iPod blueprint state: current song volume battery life behavior: power on/off change station/song change volume choose random song iPod #1 state:song = "1,000,000 Miles"volume = 17battery life = 2.5 hrs behavior:power on/offchange station/songchange volumechoose random song iPod #2 state:song = "Letting You"volume = 9battery life = 3.41 hrs behavior:power on/offchange station/songchange volumechoose random song iPod #3 state:song = "Discipline"volume = 24battery life = 1.8 hrs behavior:power on/offchange station/songchange volumechoose random song creates 11

Abstraction

abstraction: A distancing between ideas and details.

We can use objects without knowing how they work.

abstraction in an iPhone: You understand its external behavior (buttons, screen).

You may not understand its inner details,

and you don't need to if you just want to use it. 12

Our task

In the following slides, we will implement a

Pointclass as a way of learning about

defining classes.

We will define a type of objects named Point.

Each Pointobject will contain x/y data called fields. Each Pointobject will contain behavior called methods.

Client programswill use the Pointobjects.

Pointobjects (desired)

Point p1 = new Point(5, -2);

Point p2 = new Point(); // origin, (0, 0)

Data in each Pointobject:

Methods in each Pointobject:

Method nameDescription

toString()returns a String representation of this Point setColor(Color c)Set this Point's color distance(Point p)how far away the point is from point p draw(Graphics g)displays the point on a drawing panel

Field nameDescription

xthe point's x-coordinate ythe point's y-coordinate 14

Pointclass as blueprint

The class (blueprint) will describe how to create objects. Each object will contain its own data and methods.

Point class

state: int x, y behavior: setLocation(int x, int y) translate(int dx, int dy) distance(Point p) draw(Graphics g)

Point object #1

state:x = 5, y = -2 behavior:setLocation(int x, int y)translate(int dx, int dy)distance(Point p)draw(Graphics g)

Point object #2

state:x = -245, y = 1897 behavior:setLocation(int x, int y)translate(int dx, int dy)distance(Point p)draw(Graphics g)

Point object #3

state:x = 18, y = 42 behavior:setLocation(int x, int y)translate(int dx, int dy)distance(Point p)draw(Graphics g) 15

Clicker 2 What is output by the following code?

Point p1 = new Point();

Point p2 = new Point();

System.out.print(p1 == p2);

A.Syntax error

B.Runtime error

C.false

D.true

E.no output

16 17

Object state:

Fields

Point class, version 1

public class Point { private int x; private int y;

Save this code into a file named Point.java.

The above code creates a new type named Point.

Each Pointobject contains two pieces of data:

an intnamed x, and an intnamed y.

Pointobjects do not contain any behavior (yet).

Fields

field: A variable inside an object that is part of its state.

Each object has its own copy of each field.

Declaration syntax:

access_modifiertypename;

Example:

public class Student { // each Student object has a name and // gpa field (instance variable) private String name; private double gpa; }19

Accessing fields

Other classes can access/modify an object's fields. depending on the access modifier access:variable.field modify:variable.field=value;

Example:

Point p1 = new Point();

Point p2 = new Point();

System.out.println("the x-coord is " + p1.x); // access p2.y =13; // modify 20

A class and its client

Point.javais not, by itself, a runnable

program.

A class can be used by clientprograms.

PointMain.java(client program)

public class PointMain { main(String args) {

Point p1 = new Point();

p1.x = 7; p1.y = 2;

Point p2 = new Point();

p2.x = 4; p2.y = 3;

Point.java(class of objects)

public class Point { int x; int y; x7y2 x4y3 21
22

Object behavior:

Methods

Client code redundancy

Suppose our client program wants to draw

Pointobjects:

// draw each city

Point p1 = new Point();

p1.x = 15; p1.y = 37; g.fillOval(p1.x, p1.y, 3, 3); g.drawString("(" + p1.x + ", " + p1.y + ")", p1.x, p1.y); To draw other points, the same code must be repeated.

We can remove this redundancy using a method.

Eliminating redundancy, v1

We can eliminate the redundancy with a static method: // Draws the given point on the DrawingPanel. public static void draw(Point p, Graphics g) { g.fillOval(p.x, p.y, 3, 3); g.drawString("(" + p.x + ", " + p.y + ")", p.x, p.y); mainwould call the method as follows: draw(p1, g); 24

Problems with static solution

We are missing a major benefit of objects: code reuse.

Every program that draws Points would need a draw

method.

The syntax doesn't match how we're used to using

objects. draw(p1, g); // static (bad) The point of classes is to combine state and behavior. The drawbehavior is closely related to a Point's data.

The method belongs insideeach Pointobject.

p1.draw(g); // inside the object (better)25

Instance methods

instance method(or object method): Exists inside each object of a class and gives behavior to each object. public typename(parameters) {quotesdbs_dbs14.pdfusesText_20

[PDF] Topic 27 classes and objects state and behavior

What is the difference between a class and an object in Java?

What is the purpose of classes and objects in Java?

What data is associated with a class or object in Java?

How do I use classes to create objects in Java?

Topic 27

Copyright Pearson Education, 2010

Based on slides by Marty Stepp and Stuart Reges

Object Oriented Programming

What is a class?

Object Oriented Programming

In other words break the problem up based

Not the only way

One of many different kinds of strategies or

Clicker 1

What kind of assignment handout

A.A long assignment handout

B.A short assignment handout

Example -Monopoly

If we had to start

Classes Needed:

A programming problem

Given a file of cities' (x, y) coordinates,

150 91

Write a program to draw the cities on a

DrawingPanel, then a terrible event occurs

Ground zero x: 100

Ground zero y: 100

Area of effect: 75

A solution

Scanner input

Observations

The data in this problem is a set of points.

An alternative is to store them as Point

A Pointwould store a city's x/y data.

We could compare distances between Points

Each Pointwould know how to draw itself.

The driver program would be shorter

Clients of objects

Example: Zombiesis a client of DrawingPanel

Zombie.java(client program)

DrawingPanel.java(class)

Classes and objects

1.A program / module, or

2.A template for a new type of objects.

The DrawingPanelclass is a template for

Blueprint analogy

Abstraction

We can use objects without knowing how they work.

You may not understand its inner details,

Our task

In the following slides, we will implement a

Pointclass as a way of learning about

We will define a type of objects named Point.

Client programswill use the Pointobjects.

Pointobjects (desired)

Point p1 = new Point(5, -2);

Point p2 = new Point(); // origin, (0, 0)

Data in each Pointobject:

Methods in each Pointobject:

Method nameDescription

Field nameDescription

Pointclass as blueprint

Point class

Point object #1

Point object #2

Point object #3

Clicker 2 What is output by the following code?

Point p1 = new Point();

Point p2 = new Point();

System.out.print(p1 == p2);

A.Syntax error

B.Runtime error

C.false

D.true

E.no output

Object state:

Fields

Point class, version 1

Save this code into a file named Point.java.